The phenomenon of nuclear magnetic resonance (Nuclear Magnetic Resonance, NMR) is, shortly after its discovery in 1946, applied in fields, such as physics, chemistry, material science, life science and medical science. In 1950s, the nuclear magnetic resonance came into use in the fossil oil and natural gas industry, and originally applied to the field of oil reservoir rock physics. A nuclear magnetic resonance logging instrument can utilize the nuclear magnetic resonance principle to detect stratum information around the borehole, and have unique capabilities of qualitative recognition and quantitative evaluation for the reservoir fluid.
A probe is one of the important parts in the nuclear magnetic resonance logging instrument, and the structure of the probe determines key performances, such as a measuring mode of the instrument, a nuclear magnetic resonance region and nuclear magnetic resonance signal intensity. The nuclear magnetic resonance logging instrument probe mainly includes a magnet and an antenna, the magnet can form a static magnetic field for polarizing a spin hydrogen proton, and the antenna can emit a radio frequency field for reversing the spin hydrogen proton, and after the radio frequency field is removed, the spin hydrogen proton starts to precess along the static magnetic field, and thereby generates an nuclear magnetic resonance inductive signal, and the stratum situation can be analyzed by detecting the nuclear magnetic resonance inductive signal.
The existing nuclear magnetic resonance logging instrument probe usually adopts a column-shaped magnet, both rounded sides of the magnet are an N pole and a S pole, respectively, the magnetic field distribution is formed by closed magnetic lines of force pointing from the N pole to the S pole, the antenna surrounds the magnet, and can excite polarized stratum region all around the borehole by 360°, so that there is no detection blind zone around the borehole, and multi-frequency multi-slice measurement can be performed, but the signal obtained by measurement is only an average signal of signals in the 360-degree stratum. Accordingly, the nuclear magnetic resonance logging instrument probe in the prior art only can perform signal detection in radial depth dimension and axial depth dimension, but has no capability to detect signals in the circumferential multi-azimuth sensitive area.